Method and control system for a refrigeration system and refrigeration appliance including compressor associated with suction line and refrigerated compartment

ABSTRACT

A control method for a refrigeration system ( 10 ), with the refrigeration system ( 10 ) including at least one compressor ( 1 ) associated with at least one pair of suction lines (L 2 , L 3 , . . . L N ), with each of the suction lines (L 2 , L 3 , . . . L N ) respectively associated with at least one refrigerated environment (C 1 , C 2 , . . . C N ). The method includes generating a system equivalent (S eq ) to the refrigeration system, with the equivalent system (S eq ) comprising at least one control parameter (P C1 , P C2 , . . . P CN ) associated with each of the refrigerated environments (C 1 , C 2 , . . . C N ). A control system for a refrigeration system and a refrigeration appliance are also described.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority under 35 USC § 119 to Brazilian Patent Application No. BR102018011553-7 filed Jun. 7, 2018, and the entire disclosure of said application is hereby expressly incorporated by reference into the present application.

FIELD

This invention refers to a method and control system for a refrigeration system. More specifically, it addresses a method and control system for a refrigeration system that uses a compressor working on more than one suction line. It also addresses a refrigeration appliance.

DESCRIPTION OF THE STATE OF THE ART

Most refrigeration appliance used today for storing foods at low temperatures (i.e., refrigerators) have at least two refrigerated environments, consisting basically of a freezer and a chiller (chiller compartment).

In order to cool these compartments, a double suction compressor may be used, meaning compressors that comprise two gas suction lines, wherein each suction line is associated respectively with a compartment to be cooled, such as a chiller and freezer, for example.

As the capacity demand for each compartment differs, and also because they perform different functions, some solutions have been developed in order to respond to the needs of each situation and particular context, designed mainly to provide independent refrigeration capacity control of refrigerated environments, in other words, the possibility of controlling the temperature of one environment without affecting the temperature of the adjacent environment.

A possible form of action lies in controlling certain compressor parameters, such as its operating rotation and operating fraction (the valve opening time defines how long each suction line will operate).

A possible form of control is thus based on control of the above-mentioned valve through the temperature in one of the compartments, such as the chiller, for example. As a result, control of this valve will alter the temperature of the chiller compartment. The temperature of the freezer is controlled through the compressor rotation action.

However, this proposal offers the disadvantage that, when the controller is activated in a first compartment where a disturbance occurs, a second compartment is also impacted by this same control situation. Ideally, the actuation (correction) should occur only in the first compartment where the disturbance occurred.

In other words, the solution described above does not constitute a sturdy system that can isolate the control of one compartment from the others. It comprises a system that is directly affected by external disturbances and thus does not produce the desired response to such disruptions (external disturbances) that occur.

In the system as described above, when there is a disturbance (i.e. an increase in the thermal load) in the first compartment, the temperature in the second compartment is also affected. This is due to the need for temperature correction in the first compartment by the disturbance in the system, which in fact functions in both compartments, when it should function only in the first compartment.

As a result, the state of the art does not include a refrigeration system control method suitable for controlling the temperature of two (or more) compartments independently, through a compressor working on more than one suction line.

The state of the art comprises the optimization of compartment temperature control when applied to a compressor with a single suction inlet that results in temperature variations in the compartments, when activated, in order to attenuate disturbances in one of the compartments.

SUMMARY AND OBJECTIVES OF THE INVENTION

In this context, in order to surmount problems known the state of the art as mentioned above, this invention proposes a sturdy control system for independent temperature control in at least two different compartments in a refrigeration appliance.

Furthermore, this invention also proposes the implementation of a control method for a refrigeration system that uses a single compressor associated with at least two compartments. Obviously, the reference to two compartments may not be construed as a constraint on this invention, whereby the teachings proposed may be applied perfectly well to refrigeration systems comprised of two or more refrigerated compartments, as addressed in greater detail below.

When applied to a system that comprises two environments to be refrigerated (two evaporators), the proposed method is based on modeling the compressor as two independent virtual compressors; in other words, with the proposed methodology, it is possible to control a single compressor that works like two compressors, thus allowing it to function in only one of the refrigerated environments.

In a beneficial manner, the implementation of a system and method as proposed allows temperature correction in response to a disturbance in a compartment while not affecting the temperature in the other compartment; in other words, the proposed system and method allow independent temperature control in the compartments of a refrigeration appliance.

Similarly, when applied to a system that comprises more than two environments to be refrigerated (more than two evaporators), the proposed method is based on modeling the compressor into independent virtual compressors, wherein each virtual compressor is associated with a single evaporator (or chiller compartment). Thus, with the proposed methodology, it is possible to control a single compressor that functions as several independent compressors, consequently controlling the temperature of each evaporator independently.

A first objective of this invention is to provide a control system for a refrigeration system fitted with a compressor that works on more than one suction line.

A second objective of this invention is to provide a control system for handling the temperatures of at least two different compartments in a refrigeration appliance.

A third objective of this invention is to provide a control method for a refrigeration system with a compressor with two (or more) suction lines, wherein this compressor is modeled as two (or more) virtual compressors, with the said equivalent (virtual) compressors constituting an independent compressor or each the refrigerated environments or cooling circuits.

A fourth objective of this invention is to provide a system and control method suitable for providing independent control of at least two compartments in a refrigeration system with a single compressor fitted with at least two suction lines.

A fifth objective of this invention is to provide a system and control method comprising at least one control parameter associated with each of the refrigerated environments.

A sixth objective of this invention is to establish a ratio for the control parameters, the compressor rotation and the compressor control valve opening time for each suction line.

Another objective of this invention is to provide a methodology and system that can function in refrigeration systems comprised of two or more evaporators.

The objectives of this invention are attained through a control method for a refrigeration system, with the refrigeration system comprising: at least one compressor and at least one pair of suction lines, with each of the suction lines respectively associated with at least one refrigerated environment, wherein the method comprises the steps of: generating compressors that are equivalent to the compressor, with the equivalent compressors comprising at least one control parameter associated with each of the refrigerated compartments.

It also addresses a control method for a refrigeration system that comprises the steps of: establishing a reference temperature for each of the refrigerated environments, defining at least one variation (error) rate between a current temperature and a reference temperature for each of the refrigerated environments, defining at least one control parameter from the variation rates, associated with each of the refrigerated environments.

The objectives of this invention are also attained through a refrigeration system control system, with the refrigeration system comprising: at least one compressor fitted with at least one pair of suction lines, with each of the suction lines respectively associated with at least one refrigerated environment (compartment), whereby the control system also comprises: at least one control parameter associated with each refrigerated environment, obtained from at least one control loop associated with each refrigerated environment.

This also addresses a refrigeration appliance, according to the teachings of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described in greater detail below, based on an example of an embodiment demonstrated in the drawings. The Figures show:

FIG. 1—is a representation of a refrigeration system suitable for absorbing the teachings of this invention;

FIG. 2—is a representation of a refrigeration system as set forth in the teachings addressed in this invention, with two hypothetical compressors, each independently controlling the refrigeration capacity of a compartment;

FIG. 3—is a representation of the equivalent control system obtained through the teachings of this invention, wherein an independent equivalent system is noted, for each of the refrigerated environments;

FIG. 4—is a representation of the way of obtaining a control signal through a control loop addressed in this invention;

FIG. 5—presents graphic illustrations of the rotation parameters of the refrigerated environments as a function of time, the reference and current temperature values of one of the refrigerated environments as a function of time, and the control signal obtained, as set forth in the teachings of this invention;

FIG. 6—illustrates an additional representation of a refrigeration system suitable for absorbing the teachings of this invention;

FIG. 7—is an additional representation of a refrigeration system suitable for absorbing the teachings of this invention, wherein the said system is fitted with multiple refrigerated compartments;

FIG. 8—is an additional representation of a refrigeration system suitable for absorbing the teachings of this invention, wherein the said system comprises two refrigerated compartments.

DETAILED DESCRIPTION OF THE INVENTION

In the initial mention of FIG. 1, this invention refers to a control method for a refrigeration system 10, more specifically, a control method for a refrigeration system 10 that comprises a compressor 1. In a non-limiting embodiment, the compressor 1 may be configured as a double suction compressor, as shown in FIG. 1. Nevertheless, it is stressed that the teachings proposed herein are not limited to their application in a double suction compressor, whereby any compressor known at the state of the art is suitable for embodying the concepts proposed herein.

In general terms, the compressor 1 must be understood as the compressor associated with at least two suction lines, such as compressor 1 shown in FIGS. 1, 6, 7 and 8. It is thus noted that compressor 1 comprises at least a first suction line L₁ and a second suction line L₂. According to the teachings of this invention, suction lines L₁, L₂ . . . L_(N) are thus understood as “branches” of the refrigeration system 10, associated with each of the refrigerated compartments (evaporators).

As already mentioned, the compressor 1 may be associated with two or more suction lines L₁, L₂ . . . L_(N), as shown in the illustrations of the refrigeration systems 10 in FIGS. 6, 7 and 8. Furthermore, such suction lines L₁ and L₂ may be arrayed in series (FIG. 6) or in parallel (FIGS. 1, 7 and 8). Furthermore, distribution valves with any configuration known at the state of the art may be used in the illustrated refrigeration systems 10. Moreover, the distribution valves may be arrayed inside the compressor or external it, with valve placement not being considered as a constraint on this invention.

Furthermore, in the embodiment of this invention illustrated in FIG. 1, the compressor 1 is associated with at least one pair of refrigerated environments (compartments), such as the compartments in a refrigeration appliance (either commercial or residential). Consequently, and with reference to FIG. 1, it is understood that the first suction line L₁ is associated with a first compartment C₁ and the second suction line L₂ is associated with a second compartment C₂, wherein each of the compartments C₁ and C₂ is comprised of a separate evaporator. In a non-limiting embodiment, the first compartment C₁ may represent the chiller and the second compartment C₂ may represent the freezer of a refrigeration appliance 20.

It is stressed that the teachings of this invention may also be absorbed by refrigeration systems comprised of more than two refrigerated compartments C₁, C₂ . . . C_(N), as shown in FIG. 7. Furthermore, the arrangement of the second compartment C₂ and the first compartment C₁, as shown in FIG. 1, may not be considered as a constraint on this invention.

Moreover, arrangements are fully valid wherein both the first compartment C₁ and the second compartment C₂ constitute the chiller (or freezer) of a refrigeration appliance 20.

In general terms, the refrigerated compartments C₁, C₂, . . . C_(N) must be understood as the cooling circuits of the compressor 1.

As already mentioned previously, it is known that one of the challenges found at the state of the art consists of controlling the temperatures in each compartment C₁, C₂ . . . C_(N) when so-called thermal disturbances occur in the refrigeration system 10 (for example, opening doors, storing hot products, among others).

Consequently, taking FIG. 1 as a reference, the challenge arises of avoiding the so-called crossover effect: in other words, controlling the temperature in the first compartment C₁ (in this case, the chiller) with no temperature variations in the second compartment C₂ (in this case, the freezer), in other words, without temperature variations in the chiller also causing temperature variations in the freezer.

This invention encompasses a control methodology for the refrigeration system 10 that allows independent temperature control in refrigerated compartments C₁ and C₂, thus avoiding the crossover effect for temperature control.

More specifically, and with regard to FIG. 1, this invention initially proposes to model a compressor 1 as two fictitious compressors, thus allowing independent control of the control parameters of each of these equivalent compressors, in order to send a control signal to compressor 1 and thus adjust the temperatures of each of the refrigerated environments.

This invention is thus based on the possibility of representing a compressor fitted with at least two suction lines L₁, L₂ on at least two equivalent compressors (with each equivalent compressor linked to a suction line of the compressor 1) that can be controlled independently.

Pursuing a better description of the invention, a theoretical approach is valid for the equivalent compressors managed (generated) through compressor 1.

With regard to FIG. 2, a theoretical refrigeration system 10 is initially considered, comprised of two refrigerated environments C_(1′) and C_(2′), two evaporators (not shown) and also using two compressors 1′ and 1″.

Considering the mass flow ({dot over (m)}) equation for each of the environments (meaning each one of environments C_(1′) and C_(2′)) of the refrigeration system 10, leads to (Equation I): {dot over (m)} _(1=V) _(SW) _(·ρ) ₁ _(·N) ₁ ; and {dot over (m)} _(2=V) _(SW) _(·ρ) ₂ _(·N) ₂ ,

wherein:

{dot over (m)}₁ and {dot over (m)}₂=mass flow rate imposed by the compressor in each of suction lines L_(1′) and L_(2′), respectively.

V_(sw)=volumetric displacement of the compressor;

ρ₁ and ρ₂=refrigerant fluid density for each suction line; and

N₁ and N₂=compressor rotation 1″ (first compartment C1′) and 1′ (second compartment C2′), respectively.

Consequently, based on the mass flow rate equations for the scenario using two independent compressors 1′ and 1″, an attempt was made to adapt these equations to the scenario using a single double suction compressor 1, thus constituting an ideal scenario of full independence between each of suction lines L₁ and L₂ of the double suction compressor 1.

Thus, Equation I was adapted to the double suction compressor 1 shown in FIG. 1 (Equation II): {dot over (m)}=V _(sw)·ρ₁ ·N _(C)·DC+V _(sw)·ρ₂ ·N _(C)·(1−DC),

wherein:

N_(C)=actual rotation of the compressor 1;

DC=Duty Cycle=Cycle Ratio=operating fraction=ratio between the time that the compressor operates on suction line L₁ and the total completion time of a switch cycle for both suction lines;

(1−DC)=ratio between the time that the compressor operates on suction line L₂ and the total completion time of a switch cycle for both suction lines. In a double suction compressor, it is known that the sum of the Duty Cycle (DC) for both lines is equal to 1.

Consequently, Equation II may also be presented in the following manner (Equation III): {dot over (m)}=V _(sw)·ρ₁ ·N ₁ +V _(sw)·ρ₂ ·N ₂,

wherein:

N₁=N_(C)·DC (based on Equation II), and

N₂=N_(C)·(1−DC), also based on Equation II.

As a result, Equation III may be simplified in order to show that the mass flow rate of the double suction compressor ({dot over (m)}) is equal to the mass flow rate of the first suction line L₁ ({dot over (m)}₁) added to the mass flow rate of the second suction line L₂ ({dot over (m)}₂). In other words, the total mass flow rate ({dot over (m)}) is equal to the sum of the mass flow rate ({dot over (m)}) of each of the suction lines.

Consequently, a relation is established between the hypothetical compressor rotation applied to the first suction line L₁ and the hypothetical compressor rotation applied to the second suction line L₂, whereby, based on Equation (II): {dot over (m)}=V _(sw)·ρ₁ ·N _(C)·DC+V _(sw)·ρ₂ ·N _(C)·(1−DC)  (Equation II), and N ₁ +N ₂ =N _(C)·DC+N _(C)·(1−DC)  (Equation IV)

Simplifying Equation IV leads to: N ₁ +N ₂ =N _(C)  (Equation V)

It is stressed that the representation of Equation IV disregards the V_(sw), ρ₁ and ρ₂ values, as the purpose of this modeling consists of finding a relation between hypothetical rotations of each suction line in function of the actual rotation of the double suction compressor and its Duty Cycle (Cycle Ratio).

Having determined that N₁+N₂=N_(C) (Equation V), the Duty Cycle may then be modeled, based on Equation II, which showed that N₁=N_(C·)DC. This consequently leads to:

$\begin{matrix} {{D\; C} = {\frac{N_{1}}{N_{C}}.}} & \left( {{Equation}\mspace{14mu}{VI}} \right) \end{matrix}$

Thus, based on Equation V (shown below), it is clear that compressor 1 as shown in FIG. 1 may be represented as an equivalent system controlled through its hypothetical rotation with each of the suction lines L₁ and L₂. In other words, the double suction compressor 1 may be represented as a system equivalent to two compressors, wherein each of these compressors works on a single suction line. This thus makes it possible to obtain a control methodology for the double suction compressor with independent control of each of the suction lines. N ₁ +N ₂ =N _(C)

Similarly, Equation VI (shown below) allows the double suction compressor 1 Duty Cycle to be linked to the first suction line L₁ rotation, in other words, N₁, and also the double suction compressor (N_(C)) rotation, as:

${D\; C} = \frac{N_{1}}{N_{C}}$

This consequently leads to a Duty Cycle value for the first suction line L₁ (DC₁=N₁/N_(C)) and obviously a Duty Cycle value for the second suction line L₂(DC₂=1−DC₁). This consequently gives the compressor valve operating times on each of the suction lines.

Thus, based on Equations V and VI set forth above, this invention addresses a control method for a refrigeration system 10 that allows independent control of the temperature in each of the refrigerated compartments C₁ and C₂, thus avoiding improper temperature variations in one of the compartments.

As already mentioned previously, the above modeling is not limited to a scenario where the refrigeration system is comprised of only two refrigerated compartments C₁, C₂, whereby the teachings of this invention may be applied perfectly well to refrigeration systems comprised of more than two compartments C₁, C₂ . . . C_(N), as shown below. Reference is made to FIG. 7:

Similar to Equation I, there is a mass flow rate ({dot over (m)}) equation N for refrigerated compartments C₁, C₂ . . . C_(N): {dot over (m)} _(1=V) _(SW1) _(·ρ) ₁ _(·N) ₁ ; {dot over (m)} _(2=V) _(SW2) _(·ρ) ₂ _(·N) ₂ ; and {dot over (m)} _(N=V) _(SWN) _(·ρ) _(N) _(·N) _(N) ;

Similar to Equation II, there is: {dot over (m)}=V _(sw)·(ρ₁ ·N _(C)·DC₁+ρ₂ ·N _(C)·DC₂+ . . . ρ_(N) ·N _(C)·DC_(N)),

wherein:

N_(C) refers to the compressor rotation associated with N suction lines, such as for compressor 1 as shown in FIG. 7.

Similar to Equation III, there is: {dot over (m)}={dot over (m)} ₁·DC₁ +{dot over (m)} ₂·DC₂ + . . . {dot over (m)} _(N)·DC_(N)

From the equation equivalent to Equation II, there is Equation II (A): N ₁ =N _(C)·DC₁, N ₂ =N _(C)·DC₂, N ₂ =N _(C)·DC₂, N _(N) =N _(C)·DC_(N), Adding together N₁, N₂ and N_(N): N₁ +N ₂ + . . . N _(N) =N _(C)(DC₁+DC₂+ . . . DC_(N))

As DC₁+DC₂+ . . . DC_(N) must be equal to 1, there is: N ₁ +N ₂ + . . . N _(N) =N _(C)

Furthermore, isolating DC₁, DC₂ and DC_(N) from Equation II (A):

${{D\; C_{1}} = \frac{N_{1}}{N_{C}}},{{D\; C_{2}} = \frac{N_{2}}{N_{C}}},{{D\; C_{N}} = \frac{N_{N}}{N_{C}}},$

The actual compressor rotation N_(C) is thus related to each of the hypothetical rotations linked to each of the suction lines L₁, L₂, . . . L_(N). Similarly, the Duty Cycle values are linked to each of the suction lines (DC₁, DC₂, . . . DC_(N)). In other words, the times are obtained when a refrigeration system 10 valve must operate on each suction line L₁, L₂, . . . L_(N).

It has thus been demonstrated that the proposed modeling may be applied to refrigeration systems comprising two or more suction lines.

In order to implement the teachings of this invention, a reference temperature must initially be established for each of the refrigerated compartments. Consequently, based on the representation shown in FIG. 1, a reference temperature must be established for the chiller compartment T_(REFC1) and a reference temperature for the freezer compartment T_(REFC2).

The said reference temperatures T_(REFC1) and T_(REFC2) must be understood as the ideal operating temperatures for respectively the first compartment C₁ and the second compartment C₂, and may be set directly by the user of the refrigerator (refrigeration appliance) 20 or may also be factory-set through the electronic control of the refrigerator 20, depending on its operating mode (vacation mode, fast cooling mode, energy-saving mode and others).

Thus, based on the reference temperature values T_(REFC1), T_(REFC2) set for the first compartment C₁ and the second compartment C₂, an error is defined for the current temperature in the said compartments C₁ and C₂.

More specifically and based on the second compartment C₂ shown in FIG. 1, an error Δ_(C2) is defined, related to the reference temperature of the second compartment T_(REFC2) and its current temperature T_(C2). Even more specifically, the error must be understood as the difference between the reference temperature of the second compartment T_(REFC2) and its current temperature T_(C2), in other words: ΔC₂=T_(REFC2)−T_(C2). Similarly, the error for the first compartment Δ_(C1) must be understood as: Δ_(C1)=T_(REFC1−)T_(C1). In a refrigeration system fitted with N compartments, this results in: Δ_(CN=)T_(REFCN−)T_(CN).

Based on these error rates Δ_(C1), Δ_(C2), . . . Δ_(CN), the teachings of this invention propose obtaining at least one control parameter P_(C1), P_(C2) . . . P_(CN) associated respectively with the first and second refrigerated compartments C₁ and C₂.

These control parameters P_(C1) and P_(C2) must be understood as parameters linked to the refrigeration capacity of the refrigeration system 10 in order for the current temperature of one of the compartments T_(C1) and T_(C2) to reach its respective reference temperature T_(REFC1) and T_(REFC2). In other words, it is understood that the current temperature of the first compartment T_(C1) will reach its reference temperature T_(REFC1) and the current temperature of the freezer T_(C2) will reach its reference temperature T_(REFC2).

In this embodiment of the invention, control parameters P_(C1), P_(C2) respectively represent rotation parameters N_(C1), N_(C2), associated with refrigerated compartments C₁ and C₂. Consequently, these rotation parameters N_(C1) and N_(C2) must be understood as being the respective rotation values of each of the equivalent compressors shown through the approach used in Equation V.

In this embodiment of the invention, and referring to FIG. 3, control parameters P_(C1) and P_(C2) are respectively obtained from the control loops (controllers) M_(C1) and M_(C2), wherein each control loop M_(C1) and M_(C2) is respectively associated with a refrigerated compartment C₁ and C₂.

Consequently, and based on the representation in FIG. 3 of the first compartment C₁, it is understood that the compressor rotation parameter for the first compartment N_(C1) is obtained from the control loop M_(C1) and is equivalent to a fictitious value for the equivalent compressor of the first compartment C₁ whereby the current temperature T_(C1) reaches the reference temperature T_(REFC1).

Similarly, and now considering the representation of the freezer (second compartment C₂) shown in FIG. 3, it is understood that the rotation parameter of the second compartment N_(C2) obtained from the control loop M_(C2) and is equivalent to a fictitious value for the equivalent compressor of the second compartment whereby the current temperature T_(C2) reaches the reference temperature T_(REFC2).

It is thus understood that this invention uses independent control systems for each of the refrigerated compartments, in this case the first compartment C₁ and the second compartment C₂, as shown in FIG. 3. As a result, the temperature of each of these compartments may be controlled independently, without temperature variations in one compartment affecting the temperature of the adjacent compartment.

With regard to FIGS. 1 and 3, it is understood that the proposed methodology manages (generates) independent control systems that work as fictitious compressors with each of the suction lines L₁ and L₂ of the compressor 1. In other words, the proposed methodology allows the control of a refrigeration system 10 which uses compressor 1 as though the system 10 were comprised of one compressor for suction line L₂ and one compressor for suction line L₁.

To do so, it is proposed that the independent control system of the first compartment C₁ and the independent control system of the second compartment C₂ respectively comprise control loops M_(C1) and M_(C2).

In this embodiment of the invention, such control loops M_(C1) and M_(C2) are preferably configured as proportional integral derivative controllers (PID controllers). Nevertheless, it is stressed that this characteristic may not be considered as an aspect imposing limits on this invention, as other types of controllers may be used, such as proportional, proportional integral and proportional derivative controllers, as well as fuzzy controllers.

In brief, it is stressed that any controller may be used, if able to generate a capacity (rotation) signal from an error signal (such as a temperature error signal, meaning errors Δ_(C1), Δ_(C2)).

In an alternative embodiment, the use of one type of controller is proposed for the independent control system of the second compartment (such as a PID controller) and another type of controller for the independent control system of the first compartment (such as a proportional integral controller or a fuzzy controller).

With rotation parameters N_(C1) and N_(C2) established respectively through control loops M_(C1) and M_(C2), they must now be consolidated into a control signal S, to be effectively applied in compressor 1.

Referring specifically to FIG. 3 and Equations V and VI as mentioned above, control signal S to be sent to the double suction compressor 1 is linked to a compressor operating rotation N_(C) and its Cycle Ratio (Duty Cycle).

Consequently, having obtained the independent rotation parameters for the first compartment N_(C1) and the second compartment N_(C2), an operating rotation value may be obtained for the compressor N_(C) by adding together N_(C1) and N_(C2); in other words, adding together the respective rotation of each of the fictitious compressors as indicated in Equation V: N ₁ +N ₂ =N _(C)

Similarly, the Cycle Ratio (Duty Cycle) of compressor 1 may be obtained through dividing the rotation linked to the first suction line L₁ by the compressor operating rotation N_(C), as indicated in Equation VI:

${D\; C} = \frac{N_{1}}{N_{C}}$

There is thus a Cycle Ratio linked to the first suction line L₁ (DC₁=N₁/N_(C)) and obviously a Cycle Ratio linked to the second suction line L₂ (DC₂=1−DC₁).

As a result, the control signal S corresponds to a signal effectively applied to the compressor 1 and coming from two equivalent compressors, wherein one equivalent compressor is linked to the first compartment C₁ and the other equivalent compressor is linked to the second compartment C₂. It is thus understood that the equivalent compressors respectively constitute an equivalent system of the first compartment S₁ and an equivalent system of the second compartment S₂, as shown in FIG. 3.

FIG. 4 presents a simplification of the equivalent circuit S_(eq) shown in FIG. 3, wherein a representation of the way of obtaining a control signal S through a control loop from equivalent circuits S₁ and S₂ is indicated. Note the indication for obtaining the Duty Cycle (DC) and compressor operating rotation N_(C) values, as indicated in the above-mentioned Equations V and VI.

FIG. 5 presents graphic illustrations of the rotation parameters for the first compartment N_(C1) and the second compartment N_(C2) respectively, as a function of time, the reference and current temperature values of the freezer (second compartment) as a function of time, and the compressor operating rotation N_(C) and Duty Cycle (DC) values as set forth in the teachings of this invention.

Among other factors, FIG. 5 shows that the current temperature of the freezer (second compartment) is always aligned with the reference values, although minor variations may be seen, due mainly to the type of control loop M_(C2) used.

With regard to FIG. 5, it is stressed that the rotation values of the first and second compartments N_(C1) and N_(C2) must be understood as the values obtained from the control loops M_(C1) and M_(C2), respectively.

Obviously, and as already addressed in the course of this Specification, the use of the proposed methodology in a refrigeration system fitted with two compartments C₁, C₂ does not constitute a characteristic imposing constraints on this invention.

Consequently, the concepts taught here may be applied perfectly well to a refrigeration system with N compartments, based on the following equations:

N₁ + N₂ + …  N_(N) = N_(C); ${{D\; C_{1}} = \frac{N_{1}}{N_{C}}};$ ${{D\; C_{2}} = \frac{N_{2}}{N_{C}}};{and}$ ${{D\; C_{N}} = \frac{N_{N}}{N_{C}}};$

Also knowing that DC₁+DC₂+ . . . DC_(N)=1.

Aligned with the methodology described above, this invention also addresses a control system for a refrigeration system 10. More specifically, the proposed control system comprises control parameters P_(C1), P_(C2) . . . P_(CN) that are independently associated with each of the refrigerated compartments C₁, C₂ . . . C_(N) of the refrigeration system 10, wherein the said control parameters P_(C1), P_(C2) . . . P_(CN) are obtained from the control loops M_(C1), M_(C2) . . . M_(CN) associated with each of the refrigerated environments, as shown in FIG. 3.

In one embodiment, the control parameters P_(C1), P_(C2) . . . P_(CN) are related to the refrigeration system 10 capacity parameters, whereby the current temperature T_(C1), T_(C2) . . . T_(CN) in each of refrigerated compartments C₁, C₂ . . . C_(N) respectively reaches reference temperature T_(REFC1), T_(REFC2) . . . T_(CN).

Furthermore, and seamlessly aligned with the methodology described above, the control parameters P_(C1), P_(C2) . . . P_(CN) are preferably configured as rotation parameters N_(C1), N_(C2) . . . N_(CN) associated with each of the refrigerated compartments C₁, C₂ . . . C_(N), while control loops M_(C1), M_(C2) . . . M_(CN) are preferably configured as proportional integral derivative controller (PID) controllers (in other embodiments, any controller may be used that works on an error signal).

Moreover, the control system proposed in this invention also comprises at least one electronic control configured to consolidate each of the control parameters P_(C1), P_(C2) . . . P_(CN) of the refrigerated environments C₁, C₂ . . . C_(N) into a control signal S, whereby the electronic control is also configured to send the control signal S to the compressor 1. Moreover, the control signal S is linked to at least one of either a compressor operating rotation N_(C) or a Cycle Ratio (DC) of the compressor.

As mentioned above, control signal S ensures that the current temperature T_(C1), T_(C2) . . . T_(CN) of each of the refrigerated environments reaches the reference temperature T_(REFC1), T_(REFC2) . . . T_(REFCN) for each of the environments.

The compressor operating rotation N_(C) is equivalent to the sum of rotation parameters N_(C1), N_(C2) . . . N_(CN) for each of the refrigerated environments C₁, C₂ . . . C_(N). The Cycle Ratio (DC) of the compressor is equivalent to a ratio between rotation parameter N_(C1) linked to one of the suction lines (in this case the first suction line L₁) and the compressor operating rotation N_(C).

This consequently addresses a method and control system for a refrigeration system 10 that uses a compressor 1 operating on more than one suction line, allowing independent control of each of the refrigerated compartments C₁, C₂ . . . C_(N).

Consequently, this invention allows the refrigeration system 10 using a single compressor to be transformed into an equivalent circuit fitted with two or more fictitious compressors, wherein each fictitious compressor is linked to a suction line; in other words, each fictitious compressor is linked to a refrigerated environment.

As a result, the temperatures of the refrigerated environments may be controlled in a completely independent manner, thus ensuring that actions raising/lowering the temperature in one compartment do not affect the temperature in the adjacent compartment.

It is valid to stress that the reference to two refrigerated environments may not be considered as a characteristic imposing constraint on this invention, whereby the teachings proposed herein may be applied in valid embodiments to an assortment (two or more) of refrigerated environments in a refrigeration system.

Along these lines, the teachings of this invention may be applied to the refrigeration system 10 as shown in FIG. 6, wherein the said refrigeration system is comprised of a first refrigeration system (condenser 1-evaporator 1) and a second refrigeration system (condenser 2-evaporators 2 and 3). In this case, the teachings proposed herein may be applied perfectly well to the second refrigeration system (condenser 2-evaporators 2 and 3).

Moreover, the methodology described here may be applied to refrigeration systems 10 whose suction lines are arrayed in series or in parallel, with this not constituting a characteristic imposing constraints on the invention.

Moreover, the configuration and distribution of the valves in the refrigeration system 10 do not constitute characteristics imposing constraints on this invention, whereby such valves may be arrayed inside or outside the compressor 1.

Furthermore, the reference to control parameters P_(C1), P_(C2) . . . P_(CN) as being respectively rotation parameters N_(C1), N_(C2) . . . N_(CN) of refrigerated environments C₁, C₂ . . . C_(N) may also not be considered as a characteristic imposing constraints on this invention. In other embodiments, control parameters P_(C1), P_(C2) . . . P_(CN) may represent any parameter of the compressor 1 able to alter the refrigeration capacity of the system 10, such as: rotation, frequency, power, displaced gas volume and refrigerant fluid density, for example.

It is also stressed that the teachings of this invention are preferably applied to refrigeration systems that use variable capacity compressors. However, the concepts proposed herein may be used perfectly well with fixed capacity compressors (ON/OFF compressors), merely activating Cycle Ratio (Duty Cycle) of the compressor in order to do so, as it is not possible to alter the rotation levels of this compressor. This means that only the terms described above in Equation VI may be considered for fixed capacity compressors.

Furthermore, although a refrigeration system absorbing the teachings of this invention may include certain particularities, this in no way affects the methodology described above. For instance, the compressor gas distribution valve may be located inside or outside the compressor casing, and the compressor used may have only one or multiple rotation levels.

Finally, one of the variables in Equations V and VI (and their equivalents for a system with N refrigerated compartments) may be defined perfectly well as a constant variable (for example, the rotation of one of the refrigerated compartments), is introducing desired adaptations to the refrigeration system control method.

This consequently addresses a method and control system for a refrigeration system 10 using a compressor 1 that operates on more than one suction line L₁, L₂ . . . L_(N), allowing each of the suction lines L₁, L₂ . . . L_(N) of the compressor 1 to be controlled independently and thus ensuring that the temperature control of one compartment does not affect the temperature control of the adjacent compartment, thus avoiding the so-called temperature control crossover effect. This also addresses a refrigeration appliance 20 that encompasses the teachings of this invention.

Having described an example of a preferred embodiment, it must be understood that the scope of this invention encompasses other possible variations, being limited only by the content of the appended Claims, with possible equivalents included therein. 

The invention claimed is:
 1. A control method for a refrigeration system (10), the refrigeration system (10) comprising at least one compressor (1) and at least one pair of suction lines (L₁, L₂ . . . L_(N)), with each of the suction lines (L₁, L₂ . . . L_(N)) respectively associated with at least one refrigerated compartment (C₁, C₂, . . . C_(N)), wherein the method comprises: generating models of equivalent compressors for each suction line (L₁, L₂ . . . L_(N)), such that a single compressor corresponding to the at least one compressor (1) and associated with the at least one pair of suction lines (L₁, L₂ . . . L_(N)) is modeled as duplicate compressors equivalent to each other, with the equivalent compressors being modeled so as to operate at one or more control parameters (P_(C1), P_(C2) . . . P_(CN)) associated with each of the refrigerated compartments (C₁, C₂, . . . C_(N)), wherein the equivalent compressors are independent of each other, and each modeled compressor (1) is only associated with a respective suction line of the plurality of suction lines (L₁, L₂ . . . L_(N)).
 2. The method according to claim 1, wherein each of the equivalent compressors that are modeled corresponds to an independent compressor for each of the refrigerated compartments (C₁, C₂ . . . C_(N)).
 3. The method according to claim 2, wherein the control parameters (P_(C1), P_(C2), . . . P_(CN)) are linked to the refrigeration system (10) capacity parameters, whereby a current temperature (T_(C1), T_(C2), . . . T_(CN)) in each of the refrigerated compartments reaches the respective reference temperature (T_(REFC1), T_(REFC2), . . . T_(REFCN)) for each of the refrigerated compartments.
 4. The method according to claim 3, wherein the control parameters (P_(C1), P_(C2), . . . P_(CN)) are independent for each of the refrigerated compartments (C₁, C₂ . . . C_(N)) and are obtained from at least one control loop (M_(C1), M_(C2), . . . M_(CN)) for each refrigerated compartment (C₁, C₂ . . . C_(N)).
 5. The method according to claim 4, wherein at least one of the control loops (M_(C1), M_(C2), . . . M_(CN)) is configured as a controller that generates a capacity signal from an error signal.
 6. The method according to claim 5, wherein the control parameters (P_(C1), P_(C2), . . . P_(CN)) are configured as at least one among rotation parameters (N_(C1), N_(C2), frequency parameters, power parameters, displaced gas volume parameters and refrigerant fluid density parameters, associated with each of the refrigerated compartments (C₁, C₂ . . . C_(N).
 7. The method according to claim 6, further comprising: consolidating each of the control parameters (P_(C1), P_(C2), . . . P_(CN)) for the refrigerated compartments (C₁, C₂ . . . C_(N)) into a control signal (S); and sending the control signal (S) to the compressor (1), whereby the control signal (S) is linked to at least one among a compressor operating rotation (N_(C)) and an operating fraction of the compressor (DC₁, DC₂, . . . DC_(N)) for each suction line (L₁, L₂, . . . L_(N)).
 8. The method according to claim 7, wherein the compressor operating rotation (N_(C)) is equivalent to the sum of the rotation parameters (N_(C1), N_(C2), . . . N_(CN)) for each of the refrigerated compartments (C₁, C₂ . . . C_(N)).
 9. The method according to claim 8, wherein the operating fraction (D_(C1), D_(C2), . . . D_(CN)) is obtained from the relation between the rotation parameters (N_(C1), N_(C2), . . . N_(CN)) one of the refrigerated compartments (C₁, C₂ . . . C_(N)) and the compressor operating rotation (N_(C)).
 10. The method according to claim 9, wherein the operating fraction (D_(C1), D_(C2), . . . D_(CN)) is equivalent to a ratio between one of the rotation parameters (N_(C1), N_(C2), . . . N_(CN)) and the compressor operating rotation (N_(C)).
 11. The method according to claim 10, wherein the operating fraction (D_(C1), D_(C2), . . . D_(CN)) is obtained from the rotation parameters (N_(C1), N_(C2), . . . N_(CN)) of the compartment with the highest reference temperature (C₁).
 12. The method according to claim 11, wherein the control signal (S) ensures that the current temperature (T_(C1), T_(C2), . . . T_(CN)) of the refrigerated compartments reaches the reference temperature (T_(REFC1), T_(REFC2), T_(REFCN)) of the refrigerated compartments (C₁, C₂ . . . C_(N)). 